In tunable diode laser absorption spectroscopy (TDLAS), a single wavelength emitted by a tunable diode laser may be used as a source to measure the absorption spectra of a material under test. Tunable lasers may be “locked” to the center of a spectral feature of interest by passing the optical signal from the tunable laser through a “sample volume” containing the material and measuring the differential absorption with a detector. The sample volume may be, for example, a cell in a laboratory or a volume in the atmosphere. By modulating the wavelength of the tunable laser, measuring the response, and computing one or more derivatives, the tunable laser may be precisely “line-locked” to the center of the desired absorption feature.
Determination of the concentration of the material under test generally requires accurate knowledge of temperature and pressure, and absorption measurements of the material under test as a function of wavelength. In many cases, it is necessary to measure the absorption at more than one wavelength to accurately determine the concentration of the material under test. Although “line-locking” techniques may precisely lock to a desired spectral feature, these techniques do not readily permit precise measurements, for example, along a side of the desired spectral feature or of another nearby spectral feature. Without such measurements, precision spectroscopy and determination of a material's concentration may not be possible.
Therefore, there exists a need for mechanisms in a laser spectroscopy system that enable the generation of at least one precisely known wavelength for determining the concentration of a material under test.